1. Field of the Invention
The present invention generally pertains to a cable reel mounted in a vehicle steering system, e.g. for automobiles. More particularly, the invention relates to a cable reel that includes a torus-shaped enclosure, defined by a fixed member (base shell) fitted with a column switch, and a mobile member (rotor) coupled with a steering wheel and mounted with the fixed member in a freely rotatable manner. The torus-shaped enclosure contains a flat cable stored in a spiraled condition. The flat cable is wound or unwound in the cable reel, in conjunction with the rotation of the rotor. The invention also concerns an improvement in a connecting structure, in which conductor elements of the flat cable are connected to external electrical systems, e.g. an airbag system.
2. Description of Background Information
As shown in FIG. 1, a prior art cable reel includes a torus-shaped enclosure 3 including a rotor 1 which rotates in conjunction with a steering wheel, and a base shell 2 immobilized with a fixed axis which is positioned in a vehicle body side. The torus-shaped enclosure contains a flat cable 4 in a spiraled condition. The flat cable 4 usually includes several conductor elements. In the prior art, there are also provided so-called xe2x80x9cinner casesxe2x80x9d that are formed into L-shape. Each inner case 5 contains narrow-width bus bars 6 (FIG. 2A) having first and second end portions. The bus bars are mutually aligned in the inner case and fixed therein. The inner cases 5 are then fixed to the rotor and/or to the base case. Two longitudinal end portions of the flat cable 4 are stripped of their coating material, so that the conductor elements are exposed at those end portions. Likewise, there are also provided outside electrical cables 7, each having an end portion stripped of its coatings, so as to yield a cable end portion. As shown in FIGS. 2A and 2B, the first end portion of each bus bar 6 of the inner case 5 is weld connected to the conductor elements of the flat cable, while the second end portion thereof is weld connected to the cable end portions of the outside electrical cables.
The above inner case 5, located at each side of the flat cable 4, includes a first leg portion 5a which extends, when in use, parallel to the conductor elements of the flat cable 4, and a second leg portion 5b perpendicular to the direction of the conductor elements of the flat cable 4. The first and second leg portions 5a and 5b carry the bus bars, which are bent along the two leg portions 5a and 5b and fixed thereon. The conductor elements at one end portion of the flat cable 4 are superposed on the bus bars 6 carried on the first leg portion 5a, and fixed thereon by classical or ultrasonic welding. Likewise, the bared end portions of the electrical cables 7 are superposed on the bus bars 6 carried on the second leg portion 5b, and fixed thereon by a similar welding method.
When the conductor elements and the electrical cables 7 are bonded to the bus bars 6 of the inner case 5, a cover 8 (FIG. 2b) is placed on the inner case 5, so that the end portion of the flat cable 4 and that of the electrical cables 7 are held by the inner case 5 and the cover 8.
The inner case 5 and the cover 8 flanking the end portion of the flat cable are then fitted into the enclosure formed by the rotor (mobile member 1) and the base shell (fixed member 2).
The flat cable 4 and the electrical cables 7 are thus bonded to the respective end portions of the bus bars 6. However, the flat cable 4 and the electrical cables 7 have different welding characteristics. Accordingly, when the flat cable 4 and the electrical cables 7 are welded to the bus bars 6, they require their specific horn and anvil to be equipped in the welding machine. This increases installation costs. Moreover, as the horns and anvils mounted on the welding machine must be exchanged, welding operation is very cumbersome.
Besides, as is already mentioned, the electrical cables are welded to the bus bars. Accordingly, once they are fixed, it is very difficult to rearrange the connection configuration.
In view of solving such problems, an object of the invention is to provide a cable reel, for which equipment costs less and in which connections of the electrical cables can be rearranged or modified very easily.
To this end, there is provided a cable reel structure including a fixed member, a mobile member mounted thereto, and a flat cable including conductor elements, an end portion of which is exposed, the cable reel structure being configured to receive an electrical cable having a cable terminal.
In the above structure, there are provided bus bars respectively having first and second end portions, the first end portion of each of the bus bars being fixed to a respective one of the conductor elements, the second end portion of each of the bus bars forming a bus-bar terminal.
At least one of the mobile member and the fixed member includes a corresponding connector unit having an outward opening, such that the bus-bar terminal extends through the connector unit, and the connector unit is configured to receive the cable terminal through the outward opening, such that the cable terminal can be connected to the bus-bar terminal.
The cable reel structure may further include a torus-shaped enclosure defined by the fixed member and the mobile member mounted thereto in a freely rotatable way, the torus-shaped enclosure containing a flat cable such that the flat cable can be wound or unwound in conjunction with the rotation of the mobile member.
Preferably, the bus-bar terminal is a tab-type male terminal, and the cable terminal is a female terminal press-fitted on the electrical cable.
Typically, the connector unit includes a lance and/or a retainer, configured to hold the cable terminal.
Preferably yet, the bus bars are insert-molded in a suitable resin material, and the first end portion of each of the bus bars is fixed to each of the conductor elements of the flat cable by welding, such that the second end portion of each of the bus bars forms a bus-bar terminal which projects from the resin material.
Suitably, the electrical cable to be connected to the bus-bar terminal is an electrical cable incorporated in an airbag system.
In the above construction, the outside electrical cables are not welded directly to the bus bars. Instead, the bus bars are provided with terminals, and these terminals extend into, and through, a connector unit which is formed together with the rotor and/or the base shell. The terminal of each of the bus bars is then fitted with the terminal connected to the end portion of each of the electrical cables, so that the configuration of electrical cables can be rearranged easily. Further, the bus bars are welded only to the conductor elements imbedded in the flat cable. Accordingly, a welding machine for such a cable reel needs only a single horn and anvil which are used for welding the bus bars to the flat cable. Welding operation thus becomes easier, and equipment costs are lowered.
Further, when the bus-bar terminals are formed into tab shapes, the structure or configuration of the bus bars may be greatly simplified.
Preferably, an adapter case made of a suitable resin material is formed unitarily and in one piece with the flat cable. This adapter case is then fitted into the torus-shaped enclosure defined by the rotor and/or the base shell, such that the terminal of each of the bus bars projects into the connector unit through the terminal path hole. The connector unit further includes at least one hooking device, e.g. a lance, for holding the terminal of each of the electrical cables, after the latter is fitted with the corresponding bus-bar terminal. The electrical cable terminals are thus fixedly locked with the bus bars. Furthermore, the connector unit includes a retainer which serves as a second hooking device. The bus-bar and cable terminals are thus doubly locked, so that electrical connections can be established far more reliably.
When the inventive cable reel structure is applied to an airbag system, an electrical cable connected to an airbag is fitted into the connector unit located at the side of the rotor, while an electrical cable connected to an airbag control unit is fitted into the connector unit located at the side of the base shell. Typically, electrical connections in the airbag system must satisfy a stringent reliability requirement. To respond to this requirement, the bus-bar terminal and the cable terminal are now inserted directly into the connector unit and connected therein, instead of the connectors themselves being fitted with each other, and thus their terminals being connected to each other.
In such a construction, when the bus-bar terminal welded to the flat cable is not correctly fitted into the connector unit, rotation of the mobile member will generate rattling noises. This phenomenon gives another advantage of detecting mismatching of the bus-bar terminal.